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Friday, February 4, 2011

On that same gray day in early December that MOH and I found flow-banded rhyolite, brecciated rhyolite, tuff, fossils, and Earthscope, we made our way up the wide, gravelled, but unmarked road to the fault scarp on Fairview Peak. The unmarked road we took is here (Google Street View); the main road marked by the BLM "Earthquake Faults" sign is here. We took the unmarked road primarily because I'd never driven it. I don't know which road is best; the unmarked road goes by a strange government installation with warning signs and a robot that may come out onto the road every now and then, judging by tracks we saw.

The view in the first photo above looks southward from a parking area the end of a graded loop road, shown here in Street View. This same loop road is also shown on the second Google Earth image of my fault line post.We walked uphill to stand on the fault, and were surprised to see a second fault scarp uphill from the main scarp. The photo looks straight down the main scarp, left of center; the second scarp is uphill and to the right. We then walked SSW along the fault scarp to an area where the scarp cuts through bedrock rather than just cutting alluvial fan material. This is one of the most photographed parts of the fault, simply because it's so close to the loop road. To the left (east) of the east-dipping fault scarp, you can see a little valley overgrown with straw-colored bunch grass. The valley or gully is partly erosional and partly due to a small downdrop east of the main scarp. This downdrop appears to be down-to-the-west, opposite to the down-to-the-east main scarp. A similar downdrop can be seen in the USGS photo below, a photo which at first glance appears to have been taken at the same site (it may not be the same site).

USGS Photograph of the scarp formed on Dec 16, 1954, taken by H. Benioff.

The man is standing in a gully created by the juxtaposition of the main, east-dipping scarp (here it's some 2+ meters high), and a smaller, vertical to west-dipping cut to the left of the man. The USGS picture may show the same section of the fault that I photographed; it may be a different section. I know, for example, that there's a nice exposure visible if you drive (or hike) up a lousy, very steep, two-track road located north of the good, not-so steep loop road. I think the USGS photo shows what looks like a steep, second scarp above and west (right) of the main one; that second high scarp is not seemingly present at the loop-road site, and the trees and bushes don't look quite right to me. (Two Google Earth images at the bottom of this post show the loop road and lousy road.)This is the view from that southern exposure of the scarp, with MOH for scale, looking back to the NNE, toward the little parking area at the end of the road.Here's a similar view looking northeast along the sharp, V-shaped valley, which was in part formed by down-dropping along its right (east) edge, similar to the doubly faulted valley in the USGS photo. There may be a technical term for this second, opposing scarp or faulted valley, a term I don't know. There's a great view to the northeast from the fault scarp (photo enlarges nicely), making the short hike well worthwhile. The Desatoya Mountains are the blue, snow-covered mountains on the right; the Clan Alpine Mountinas are the brownish to bluish mountains in front of them to the left and in the center. On our day's journey, we started near the southernmost visible part of the Clan Alpine Mountains. The EarthScope observatory we saw earlier is in the low hills of that southern, brownish part of the Clan Alpine Mountains. The loop road. The scarp we walked to is the whitish, slightly bent part of the scarp where it crosses a little, tree-covered hill southwest of the loop. North is to the right. The barely visible, steep, two-track road that leads to another well exposed scarp can be seen when this Google Earth image is enlarged. This road is not recommended for travel because of turning around problems at its steep upper end.

4 comments:

Very nice photos and description of the locale! I'm wondering about the USGS photo taken by Benioff in 1954 and your photo of the most photographed section of the fault...in Benioff's photo, I can't see the hill in the background. Wonder if it's the angle or just that it's not the same section of the fault. However, the trees/bushes seem to be in eerily similar positions on each side of the scarp and are bigger in your photo than in the '54 photo, which makes sense. Either way, very cool blog...looking forward to reading more!

Robert, I'm not sure if the locality in both photos is the same. That really steep second section of the fault in the USGS photo (the closest part on the right) didn't appear to be present in area I went to, and to me the trees don't look quite right, although I know lots of junipers will have grown since 1954, and all trees will have gotten larger. There is at least one other section of the fault that cuts through a hillslope similar to this one; I haven't really looked at that area closely for more than 20 years. Might have to go back!

And yes, the angle of the two photos appears to be at least slightly different, if it's the same spot.